It is known from German Auslegeschrift No. 1,770,703 to use mixtures of mutually-incompatible polyols in the production of polyurethanes, and from German Offenlegungsschrift No. 2,309,861, to use these incompatible polyol mixtures to produce foam moldings having compact surfaces. In the manner according to these references, end products having improved properties, such as, for example, improved heat resistance or improved impact strength, may be obtained.
The use of these incompatible polyol mixtures is, however, attended by a number of disadvantages in storage and processing. Even short-term storage, i.e., from a few hours up to three days, of such normally-incompatible polyols causes the mixtures to separate into two phases. Thus, before each use, the polyol mixtures must be intensively mixed again or they must be constantly mixed or circulated, in order to ensure that the mixture ratio of the components is maintained.
Various methods are known to adjust such mixtures so that a stable phase will result. According to U.S. Pat. No. 3,945,393, the phases may be precipitated by adding colloidal silica or a clay which is modified with an onium compound. Similarly, German Offenlegungsschrift No. 2,341,294 teaches the simultaneous use of inert, surface-active materials which have specific surface areas of from 10 to 800 m.sup.2 /g, such as agglomerated silica and/or a chrysotile asbestos, or an inorganic material corresponding to chrysotile asbestos in its mineral structure.
Another possibility of homogenizing several mutually-incompatible polyols resides in the simultaneous use of liquid or solutions of solid solubilizers. Thus, according to U.S. Pat. No. 4,141,852, mixtures of monomeric polyols having molecular weights of greater than 500 and polyether polyols having molecular weights of from 1800 to 7000 remain mixed with the simultaneous use of so-called "graft polypropylene ether glycols" having molecular weights of from 1500 to 3500. A stable emulsion of a high molecular weight polyol and ethylene glycol or butane diol-1,4 is prepared, according to U.S. Pat. No. 4,273,884, by simultaneously using an ethylene oxide/propylene oxide copolymer (molecular weight .gtoreq.12000). German Auslegeschrift No. 2,759,398 describes stable mixtures of poly(oxypropylene/oxyethylene)polyols (OH numbers of from 20 to 60), having certain oxyethylene contents, and ethylene glycol or butane diol. In U.S. Published Patent Application No. B471,405, mixtures of high molecular weight polyoxyalkylene polyols which have OH equivalent weights of from 650 to 3000, and, for example, ethylene glycol, are protected against separation by the simultaneous use of compounds, such as 1,2-butylene glycol, di-(1,2-butylene glycol), di-(1,2-propylene glycol) and tri-(1,2-propylene glycol). Further, those skilled in the art know that two-phase mixtures of mutually-incompatible polyols may also be adjusted to be single phase by adding a small quantity of emulsifiers, such as long-chain benzene alkyl sulphonates.
None of these prior art teachings is completely satisfactory, however. The use of solids as emulsion stabilizers may cause the abrasion of mixing apparatus and the stabilizing effect itself generally subsides quite considerably after a few days. Physiological reservations have recently been advanced against asbestos materials. Additionally, the inherent catalytic activity of silica or chrysotile surface active materials, in particular, when modified with onium compounds, may also cause complications.
The simultaneous use of so-called "graft polyols", as proposed by U.S. Pat. No. 4,141,852, adds the expense of such "graft polyols", and thus reduces the economy of the process. Even when these "graft polyols" are used, the effort to create a single phase, storage-stable polyol mixture is not necessarily satisfied, as the emulsions produced according to U.S. Pat. No. 4,273,884 exhibited at least partial separation of the phases within the first 6 to 8 weeks and the reference itself states that its emulsions are only "fairly stable" anyway. Further, while the simultaneous use of di- and tri-propylene glycol, as disclosed in U.S. Published Patent Application No. B471,405, allows the production of single-phase, stable polyol mixtures, it is well known that the simultaneous use of these compounds results in a sharp decrease in the mechanical properties of polyurethane parts produced therefrom, with heat stability of the end product particularly suffering.
The use of conventional emulsifiers for maintaining stable mixtures is also attended by a number of disadvantages. In time, the emulsifiers may precipitate from the polyol mixture in a crystalline form, or they may become concentrated, for example, on the surface of the liquid. Also, these emulsifiers may change the catalytic system balance in an uncontrollable manner, or they may migrate from the finished polyurethane molding and thus drastically reduce the use properties thereof.
These problems are particularly troublesome in that there is an urgent commercial interest in polyol formulations which have a high mixed OH number and a high proportion of ethylene glycol and/or butanediol-1,4, which are completely stable in storage for a sufficiently long period of time (for a minimum of about 6 months), are optically clear, and do not contain other solid or liquid additives. Particularly, any additives which are present must not precipitate or separate in another manner, or enter into or change a reaction.
Surprisingly, it has been found that mixtures of certain polyoxyalkylene polyols and certain hydroxy compound/alkoxirane reaction products are single-phase and storage-stable within particularly wide areas. These mixtures are completely clear optically and have a high proportion of ethylene glycol or butane diol-1,4, without too high a content of undesirable alkoxylation products of ethylene glycol or butane diol-1,4, when they contain ammonium and/or metal salts of, for example, C.sub.1 -C.sub.8 mono- or poly-carboxylic acids.